Packaging refers to the process of mounting integrated circuits (dies), which are principally composed of a semiconductor within a protective body, with electric contacts of the integrated circuit connected to conductive elements extending through the body, so that the conductive elements can electrically connect the integrated circuit to other electronic circuitry. Perhaps the most common conventional packaging technique is wire bonding, in which wire bonds are formed between electrical contacts (pads) on the integrated circuit and fingers of a lead frame. A resin body is then molded around the integrated circuit and wire bonds, and the lead frame is cut to leave portions of the lead fingers projecting out of resin body, for easy connection to a PCB (printed circuit board) or other substrate.
Many variations of this technique are known, such as variations in which the integrated circuit is mounted directly on the PCB, and the wire bonds are formed directly between the PCB and the integrated circuit. In other variations, multiple integrated circuits are stacked on one surface of the PCB. In yet further variations, integrated circuits are packaged on opposite surfaces of the PCB.
Another common packaging technique employs “flip-chips”, that is, integrated circuits that have electric contacts on one of their major faces, and are adapted to be placed with that major surface directed downwardly onto a surface of the substrate, with the electric contacts of the flip-chips in register with corresponding electric contacts of the substrate. Special measures are taken to ensure that all the respective pairs of contacts meet, despite any unevenness that may exist in the surface of the integrated circuit or substrate. The space between the flip-chip and the substrate is then filled with an insulating “underfill” layer.